This invention relates to apparatus for performing high voltage testing and more particularly to apparatus for confirming that the test voltage has been properly applied to the test article for at least a predetermined minimum time period.
A high voltage or hi-pot test is commonly performed by applying a voltage of predetermined magnitude between two parts which are electrically insulated from each other in order to determine that minimum standards of the quality of electrical insulation between those parts exists. For example, during the manufacture of lead acid electric storage batteries, cell groups are hi-pot tested to verify that the separators, which provide electrical insulation between the positive and negative plates of the cell group, are properly installed and functioning. The hi-pot test typically involves applying a high voltage, for example 3000 volts, across the positive and negative plates for a predetermined minimum amount of time. An arc appearing between the positive and negative plates indicates a defective separator. If no arc appears within the predetermined minimum high voltage application period, the separators are deemed to be installed and functioning correctly.
The nature of hi-pot testing demands that the high voltage be applied between the insulated parts for at least a predetermined period of time. This insures adequate stressing of the insulating material by the applied high voltage in order to cause a break down of weak or defective regions. Such breakdown is manifested by arcing. If the high voltage is applied for less than the predetermined minimum amount of time, it is possible that a weakened or defective region of the insulation will not have time to breakdown; therefore, it will appear to the test conductor that the test results are normal even though such weakened or defective areas in fact exist.
High voltage test apparatus detects defects in electrical insulating media by sensing an increase in current through the media which, as previously stated, is caused by arcing. Such increase in current will cause the apparatus to sound an alarm, and/or in the case of an automatic test apparatus, to activate a reject cycle. It should be noted, however, that such apparatus will not detect malfunctions in the test equipment itself, for example: defective test leads; or an applied voltage of insufficient magnitude; or an absence of applied voltage altogether. Such apparatus will also not detect other malfunctions such as test probes which do nor properly contact the article under test. If one or more of these malfunctions occur, the required the test voltage will not be applied to the test article. Consequently, weakened or defective areas in the insulating material will not be stressed, and arcing, which causes rejets to be detected, will not occur. As a result, defective articles will be passed on as acceptable.